In the three final full weeks of an astronomically expensive midterm election, outside groups have spent more than $300 million trying to influence the outcome, a Sunlight analysis of campaign finance disclosures reveals. The waning days of the contest to determine control of Congress saw a growing share of that money coming from anonymous dark money groups.

The spending has been concentrated on a few nail-biter Senate races that could determine control of the chamber — the biggest prize of tomorrow’s balloting.

Sen. Pat Roberts’ reelection battle in Kansas saw the biggest uptick in interest recently as the national parties and outside committees sense the veteran Republican could lose his seat to independent challenger Greg Orman. The weekly spending in that race continued to climb even as other Senate contests saw a modicum of cooling off.

Overall, spending by super PACs and party committees still accounts for the bulk of independent spending on elections, though money spent on direct advocacy by political nonprofits (the dark money groups that don’t report donors) recently topped $145 million.

Some fancy filing footwork, meanwhile, ensures that some super PACs that spend millions influencing the vote, won’t disclosing their donors until after voters go to the polls, as the New York Times and Sunlight have reported.

We reported recently that the dark money we’ve been able to trace has gone overwhelmingly for Republican candidates and recent outlays show that trend still holding true.

Since that story, Ending Spending Inc., a conservative nonprofit organization, threw another $3.2 million at voters in the Colorado Senate race and $150,000 in to Iowa, the U.S. Chamber of Commerce dropped an additional $2.86 million on Senate battles while the Democratic Patriot Majority has shed another $1 million.

To date: Democratic-leaning outside groups have spent $338 million on direct advocacy for candidates while Republican groups accounted for $392 million by our count. That’s on top of an additional $30 million from groups we could not categorize.

For political money counters who can’t get enough of money in the midterms, visit Real-Time Federal Campaign Finance’s overview page, where you can find the numbers broken down. Want a chart for your blog or newsletter? You’ll find plenty to choose from here.